Transducer



Jan. 10, 1961 A. l. DRANETZ ETAL 2,967,956

TRANSDUCER Filed April 19, 1955 2 Sheets-Sheet 2 NVENTORS RB/PRHHM I.DRHMSTZ Hus/1 .1 C'ULL/N QTTOENE Y 2, 195 6 Patented Jan. 10, 1961TRANSDUCER Abraham 1. Dranetz and Hugh J. 'Cullin, Metuchen,

N.J., assignors to Gulton Industries, Inc, a corporation of New JerseyFiled Apr. 19, 1955, Ser. No. 502,459

4 Claims. (Cl. 310-91) Our invention relates to electro-mechanicaltransducers and in particular to those ceramic electro-mechanicaltransducers which employ a vibrating disc which is eX- cited in abending mode of resonance.

Up to now, ceramic underwater sound transducers have been of the form ofeither fiat discs or cylinders. These vibrating systems will vibrate atthe largest amplitude when they are excited at one of their resonantfrequencies (fundamental or harmonic). The common modes of resonanceutilized in disc transducers are the radial and the thickness modes andthose utilized in cylindrical transducers are the radial and lengthmodes. Disc transducers vibrating in radial and thickness mode posses aninherently'high Q, and cylindrical transducers increase in size as theresonant frequency is lowered. Since it is desirable to obtaintransducers of reasonable size with low resonant frequencies, we proposeto utilize the flexural vibrational modes of disc transducers.

Accordingly, it is a principal object of our invention to provide adisc-shaped ceramic tranducer capable of being excited in flexuralmodes.

It is a further object of our invention to provide a disc-shaped ceramictransducer which is easily manufactured and produced.

It is a still further object of our invention to provide an economicaldisc-shaped transducer of low resonant frequency and low Q.

'It is a still further object of our invention toprovide a mass-loadeddisc-shaped ceramic transducer capable of being excited in flexuralmodes.

Other objects and advantagesof our invention will be apparent during thecourse of the following description.

In the accompanying drawings, forming a part of this application, and inwhich like numerals are employed to designate like parts throughout'thesame,

Figure 1 is a plan view of .anembodiment of our invention, a

Figure 2 is a sideelevation of the embodiment of Fig ure 1, g t

Figure 3 is utilized to illustrate the stresses in a transducer which isexcited in flexural mode,

Figure 4 is a cross-sectional view of a further embodi- Figure is across-sectional view along the line 19-.

Figure 11 is a perspective view of a further embodiment of ourinvention, illustrating another method of mass loading, and

Figure 12 is a cross-sectional view along the line 12- 12.

In the drawings, wherein for the purpose of illustration, are shownpreferred embodiments of our invention, the numeral 15 designates theactive element of a ceramic transducer, 16 designates the clampingscrews, and 17 designates the electric cable. The numeral 18 designatesclamping surfaces, 19 designates ceramic transducer active elements, 20designates the electrodes, 21 designates the directions of elementstress, and 22 designates the resultant direction of motion.

The numeral 23 designates the active element of a ceramic transducer, 24designates the center support, 25 des- 'ignates the metal element of theceramic-metal sandwich and serves as the lower electrode, 26 designatesthe case and 27 designates the mass backing. The numeral 28 designatesthe sealing ring, 29 designates the active elements of a ceramictransducer, 30 designates the electrodes, and 31 designates theseparation surface. The numeral 32 designates the stress curve of anedge-clamped disc transducer, 33 designates the stress curve of anedge-supported disc transducer, 34 designates the ceramic transducerelement, 35 designates the upper electrode and 36 designates the outermass ring. The numeral 37 designates the slits in outer mass ring 36, 38designates the lower metal element of the ceramic-metal sandwich and 39designates the center support. The numeral 40 designates the cerarnictransducer element, 41 designates the upper electrode, 42 designates thelower metal element of the ceramic-metal sandwich, 43 designates theslits in the outer rim, and 44 designates the center support.

The embodiments of our invention described and illustrated utilizeceramic transducers of the titanates and in particular those which aremade largely of barium titanate. However, our invention applies equallyas well to flat-plate transducers of any shape, such as squares,rectangules, ellipses, etc. which are capable of being excited inflexural mode. Materials which are either piezoelectric,magnetostrictive, electrostrictive or the like are suitable to carry outour invention and may be employed as the active material of transducersproduced in accordance with the invention.

The embodiment of our invention illustrated in Figures 1 and 2 mayutilize either the two active elements in the sandwich construction ofFigure 3 or an active piezoelectric element backed by apiezoelectrically inert disc such as are illustrated in Figures 4, 9 and11. All the embodiments of our invention may be constructed of eithertype of transducer. The electrical connections to the active element 15of the transducer are contained in cable 17 and the active element 15 isclamped by clamps 16 around the edge of 15. When the unit is excited atthe resonant frequency of the flexural modes, the center of activeelement 15 will move in the direction 15a as illustrated in Figure 2.

Figure 3 serves to illustrate this action wherein the transducer iscomprised of two active elements 19 with electrodes 20 on each outerface and between the two separate active elements 19 suitably bonded orotherwise fixedly attached to the surfaces of 19. The electrodes areelectrically connected so that an applied voltage will cause the activeelements to stress in the directions indicated by arrows 21. If thestresses as indicated by arrows 21 are so produced, the resultant motionof the transducer will be in the direction shown by arrow 22. When thedirections of arrows 21 are reversed, the direction of arrow 22 willlikewise be reversed. The flexing of the transducer along'the line ofarrow 22 will occur at the frequency of the applied voltage. In likemanner, if the transducer is mechanically or acoustically flexed alongthe line of arrow 22, the voltage produced will be of the same frequencyor time dependence as the applied stress.

If the two active elements 19 are polarized in the same direction, thenthey should be driven in parallel. While if the two active elements 19are polarized in opposite directions, then they should be driven inseries.

In water, utilization of the flexural mode of vibration produces a broadpeak if output is plotted against frequency whereas the other modes ofvibration produce much sharper peaks. The optimum figure of merit, Q,for a transducer of a given size may be attained by suitablemass-loading of the transducer. This may be accomplished by varying theloading masses in size, position or both. Control over the acousticcoupling of the transducer may also be attained by selective isolationof portions of the transducer face which are operating out of phase withthe major portion of the face.

Figure 4 illustrates a unit produced in accordance with our inventionwherein the active element 23 is backed by a piezo-electrically inertbacking 25 to which it is securely and uniformly bonded, the wholeassembly being centersupported by support 24 which is mass backed by 27.The complete unit is enclosed in case 26 and sealed by sealing ring 28.When the active element 23 is energized by a potential, the planesurface of 23 tends to shrink and grow in accordance with the frequencyof the app-lied exciting potential. This motion of the active element 23is resisted by inert disc 25, thus causing the combined unit 23-25 tovibrate in the flexural mode. The output of this type of transducer islower than the output of a similarly sized unit containing two :activeelements such as is illustrated in Figure 3 but it is simpler to machineand construct especially since the mounting arrangement and mass backingmay be constructed of the same piece as the inert backing.

If center supporting is desired, such as is illustrated in Figure 3, themetal may be turned so that the disc portion resembles the head of amushroom supported on a stern. When this is backed with suflicient mass27, the disc is free to vibrate with a fixed center point. If edgeclamping is employed, the metal disc is made so that clamping space isprovided on the outside rim and the center is free to vibrate.

The unit illustrated in Figures and 6 utilizes rings of electrodes 30 onthe active elements 29. The spacing between these electrode rings 30should be larger than the thickness of the active elements 29. Theembodiment illustrated shows electrodes on both surfaces of activeelements 29 but this is not necessary to excitation of the elements inflexural mode; the electrodes may be mounted on one surface only or asingle active element may be employed in lieu of the two active elementsillustrated. In Figure 6, the active elements are bonded together orsuitably afiixed along the separation surface 31.

The curve 32 of Figure 7 illustrates the stress of a transducer,produced in accordance with our invention, which is edge-clamped and thecurve 33 of Figure 8 illustrates the stress of a transducer, produced inaccordance with our invention, which is edge-supported.

Figures 9 and illustrate a further embodiment of our invention whereinceramic element 34 is suitably bonded to electrode 35 and is backed bypiezoelectrically inert metallic element 38 which is center-supported bycenter support 39. These elements 38 and 39 may be of the formsdescribed in the description of the embedment of Figure 4. Outer ring 36serves to mass load the transducer and may be of the same material andturned from the same piece as 38 and 39' or all three elements may be ofdifferent materials or the same material individually fabricated andsuitably and appropriately attached or fastened together. The slots 37serve to relieve the compression in outer ring 36 when the transducervibrates flexurally.

Figures 11 and 1?. illustrate a further embodiment of our inventionwherein a ceramic-metal sandwich compris ing ,c eramieelement 40 whichis suitably bonded to electrode 41 and to metallic element 42,center-supported on center support 44 and with slots 43 around theperiphery of the ceramic-metal sandwich 40-42. These slots serve torelieve the compressional effect in the transducer when the transduceris vibrated flexurally.

In embodiments of both Figures 9 and 11, the lower metallic elements 38and 42 may be replaced by active ceramic elements such as is illustratedin Figure 3. When ceramic-ceramic sandwiches are employed, a secondelectrode must be employed on the lower face of the ceramic elementwhich replaces either of the metallic elements 38 or 42. If 42 ismetallic, as illustrated, it may be machined from the same piece as 44or the two elements 42 and 44 may be of separate pieces and suitablyaflixed together.

Sufiicient mass backing such as is shown in Figure 4 must also beemployed in the embodiments of Figures 9 and 11 and the supportstructures 39 and 44 should be similar to but need not be identical to24 of Figure 4.

While we have described our invention by means of specific examples andin specific embodiments, We do not wish to be limited thereto, forobvious modifications will occur to those skilled in the art withoutdeparting from the spirit of our invention or the scope of the subjoinedclaims. 7

Having thus described our invention, we claim:

1. An electro-mechanical transducer comprising, a substantially discshaped member including at least one substantially disc shapedpiezo-sensitive element provided with electrodes, a support secured atright angles to the center of the substantially disc shaped member andhaving transverse dimensions appreciably less than the planar dimensionsof the substantially disc shaped member for supporting the center onlyof the substantially disc shaped member, a housing therefor, meanswithin the housing connected to the support and having a mass greaterthan the mass of the support for substantially preventing longitudinalmovement of the support so as to provide a substantially stationarycenter support for the substantially disc shaped member, and means forapplying flexing forces directly to the substantially disc shaped memberfor flexing the same substantially uniformly about its substantiallystationary center, as into and out of umbrella shape.

2. An electro-mechanical transducer for converting mechanical energyinto an electrical signal comprising, a substantially disc shaped memberincluding at least one substantially disc shaped piezo-sensitive elementprovided with electrodes, a support secured at right angles to thecenter of the substantially disc shaped member and having transversedimensions appreciably less than the planar dimensions of thesubstantially disc shaped member for supporting the center only of thesubstantially disc shaped member, a housing therefor, means within thehousing connected to the support and having a mass greater than the massof the support for substantially preventing longitudinal movement of thesupport so as to provide a substantially stationary center support forthe substantially disc shaped member, and means for applying mechanicalflexing forces directly to the substantially disc shaped member forflexing the same substantially uniformly about its substantiallystationary center, as into and out of umbrella shape, for producingcorresponding electrical signals at said electrodes.

3. An electro-mechanical transducer for converting electrical energy tomechanical energy comprising, a substantially disc shaped memberincluding at least one substantially disc shaped piezo-sensitive elementprovided with electrodes, a support secured at right angles to thecenter of the substantially disc shaped member and having transversedimensions appreciably less than the planar dimensions of thesubstantially disc shaped member for supporting the center only of thesubstantially disc shaped member, a housing, means within the housingconnected to the support and having a mass greater than the mass of thesupport for substantially preventing longitudinal movement of thesupport so as to provide a substantially stationary center support forthe substantially disc shaped member, and means for applying electricalenergy to said electrodes for flexing the substantially disc shapedmember substantially uniformly about its substantially stationarycenter, as into and out of umbrella shape, for producing correspondingmechanical energy.

4. An electro-mechanical transducer comprising, a substantially discshaped member including at least one substantially disc shapedpiezo-sensitive element provided with electrodes and having a peripheralmass, a support secured at right angles to the center of thesubstantially disc shaped member and having transverse dimensionsappreciably less than the planar dimensions of the substantially discshaped member for supporting the center only of the substantially discshaped member, a housing therefor, means within the housing connected tothe support and having a mass greater than the mass of the support forsubstantially preventing longitudinal movement of the support so as toprovide a substantially stationary center support for the substantiallydisc shaped member, and means for applying flexing forces directly tothe substantially disc shaped member for flexing the same substantiallyuniformly about its substantially sta' tionary center, as into and outof umbrella shape.

References Cited in the file of this patent UNITED STATES PATENTS

